On the amplification of broad band jet noise by a pure tone excitation

Flowfield and Far Field Acoustic Amplification Properties of Heated and Unheated Jets

“…It is perhaps also supported by the broadband amplification observed, for example, in Ref. 4 where the excitation is upstream of the nozzle. Usual methods of exciting the jet upstream of the nozzle cause an attenuation of the sound at the exciting frequency.…”

“…Usual methods of exciting the jet upstream of the nozzle cause an attenuation of the sound at the exciting frequency. 4 ' 12 This has also been studied analytically by Howe. 15 In our model, the jet is excited downstream of the nozzle and, in fact, the boundary conditions are designed to simulate a flux of energy up the pipe only.…”

Aeroacoustics

“…Moore's clear visualization of these eddies that are produced in a controllable sequence cannot help but give observers the feeling that the whole subject is at a turning point. This fe eling · is reinforced by the results produced independently by Bechert & Pfizenmaier (1975) and Moore (1976) (which at first seem incredible) that the broad-band noise -of a jet can be adjusted over a wide range by weak harmonic acoustic excitation at the nozzle.…”

“…This review is intended to include those aspects of the industrial programs that have given rise to fundamental new insight and is intended also to convey the author's impression that the science of aeroaeousties has reached its most exciting stage. New developments are transforming our understanding of the problem and leading to a far more penetrating analysis of noise-control prospects; some of these, such as active control (ef Swinbanks 1973, Kempton 1976a, Moore 1976, Bechert & Pfizenmaier 1975, are full of both scientific challenge and commercial possibilities.…”

Wave Models of Turbulent Flow Over Compliant Surfaces

“…These large-scale motions are possibly the weak by-products, the nonlinear fallout of the locally controlled energetic motions, but quite possibly, and very much more excitingly, they may be more highly sensitive to the large-scale influences of otherwise weak boundary perturbations. The large-scale eddies of turbulent jet flows [1,2] are now known to be sensitive to weak external influences, as also is the sound those jet flows generate. It is yet too early to say whether boundary layer turbulence exhibits the same sensitivity and whether other large-scale, or integral, properties of the boundary layer, such as heat transfer or drag, are similarly affected.…”